Abstract
In this paper, a semi-empirical method for the prediction of rain attenuation in slant paths and terrestrial links is proposed. The method uses the same simplified model of equivalent rain cell that is the basis for the ITU-R rain attenuation prediction methods but, additionally, the concept of an effective rain rate is introduced. This allows the use of the full rainfall rate distribution for the prediction of the rain attenuation distribution and the unification of the slant path and terrestrial links prediction algorithms. The numerical coefficients in the method’s expressions were derived by multiple non-linear regressions using the experimental data currently available in the ITU-R data banks. Test results indicate that the proposed method provides significant improvement over the current ITU-R methods.
Highlights
The methods for the prediction of rain attenuation in slant path links and terrestrial links currently recommended by the ITU-R are based on simplified models for the rain field affecting the propagation path
One shortcoming of the current ITU-R methods is that the attenuation is predicted using only the measured rainfall rate exceed at 0.01% of the time
For other percentages of time, the attenuation is obtained using an extrapolation function. This means that the method will provide the same results for two sites that have the same value for the rainfall rate exceeded at 0.01% of the time, no matter if their rainfall rate distributions only coincide at this point and not for other time percentages
Summary
The methods for the prediction of rain attenuation in slant path links and terrestrial links currently recommended by the ITU-R are based on simplified models for the rain field affecting the propagation path. The basic assumption in the method is that an equivalent cell of uniform rainfall rate and length d0, randomly positioned in the great circle plane, can represent the effect of the non-uniform rainfall along the propagation path Assuming that this equivalent rain cell may intercept the link at any position with equal probability, the expression for an effective path length is calculated. To calculate the attenuation exceeded at other percentages of time between 1% and 0.001% an extrapolation formula is used [1] This represents a shortcoming of the method, as in two regions with different distributions of point rainfall rate but similar values of R0.01 the same behavior for the attenuation will be predicted. The dependence of the reduction factor on link parameters was investigated, using experimental data from concurrent long-term measurements of point rainfall rate and rain attenuation in terrestrial links available in the ITU-R databanks [34]. A correction factor rp was calculated for 0.01% of time, but for all percentages of time for which data is available, using rp
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